An infrastructure includes water supply and sewerage systems, high-pressure chemical pipelines, such as for gas and petroleum, large-scale facilities, such as high-speed railway networks, large constructions, such as long-span bridges and high-rise building, and transport equipment, such as large passenger aircrafts and automobiles. Piping is one of the important mechanisms among these facilities and equipment. A fluid, such as water, is passed through the piping. Therefore, if the piping is broken, it leads to fluid leakage. Consequently, it is necessary to instantaneously detect the leakage and repair the broken portion.
Thus, it is important to detect fluid leakage in piping as an initial action. Hereinafter, inspecting piping in order to detect fluid leakage in the piping is referred to as a leakage inspection.
A general leakage inspection is an audibility sensory inspection, in which a person catches leakage sounds. Meanwhile, in many cases, piping is installed underground or in high places. Therefore, a catching operation for the leakage sounds by a person involves a large amount of labor and risks. Thus, a technique for causing a dedicated device to perform a leakage inspection is proposed.
As one example of such a leakage inspection technique, PTL 1 describes a leakage detecting device. According to PTL 1, sounds detected around piping are converted to electric signals and the electric signals are analyzed, thereby detecting a leak. More specifically, the electric signals obtained from the acquired sounds are decomposed into different frequencies by use of a plurality of bandpass filters. Then, the amplitude of the electric signal at each frequency is compared with a threshold value. As a result, when the amplitude of the electric signal exceeds the threshold value for all of the plurality of signals, a determination is made that there is a leak.